Karoly:
There are a number of estimates of the hemispheric average temperature using different methods and different proxy data, not just the one shown … by Michael Mann and his collaborators. They all show that the period around 1000 AD was relatively warm and that the period around 1600 to 1800 was relatively cool, just as the Hockey Stick does. However, they all show that the increase in Northern Hemisphere average temperature over the twentieth century was larger than in any other century over the last millennium and that the last 30 years was likely warmer than any other 30-year period over the last 1000 years averaged over the whole Northern Hemisphere.

Happer:
The hockey-stick temperature record was conspicuously absent from the latest IPCC report, which speaks volumes. My guess is that the hockey stick started out as an honest but mistaken paper, but one welcomed by the global-warming establishment. They had been embarrassed for years by the Medieval Warm Period, when Vikings farmed Greenland, and when emissions from fossil fuels were negligible. A.W. Montford’s book, The Hockey Stick Illusion (Anglosphere Books, 2015), is a pretty good summary of what happened.

Karoly:
Science has established that it is virtually certain that increases of atmospheric CO2 due to burning of fossil fuels will cause climate change that will have substantial adverse impacts on humanity and on natural systems. Therefore, immediate, stringent measures to suppress the burning of fossil fuels are both justified and necessary.

Happer:
There is no scientific basis for the claim that increases of atmospheric CO2 due to burning of fossil fuels will cause climate change that will have substantial adverse impacts on humanity and on natural systems. If fossil fuels are burnt responsibly to limit real pollutants like fly ash, oxides of nitrogen or sulfur, heavy metals, etc., the CO2 released will be a benefit to the world. Any resulting climate change will be moderate, and there will be very major benefits to agriculture and other plant life.

Karoly:
The increase in atmospheric carbon dioxide over the past 40 years agrees very well with the increase expected from emissions associated with burning fossil fuels, land clearing, and industrial activity, less the additional uptake of carbon dioxide into the oceans and the land ecosystems due to the higher concentrations.

Happer:
…. agrees that the observed increase in CO2 concentration in the atmosphere is due to human activity: burning fossil fuels and other industrial activity.

Karoly:
Nevertheless, an overwhelming consensus of climate scientists agree that human-caused climate change is happening, and that global warming will continue throughout the current century, with many adverse impacts on human and natural systems.

Happer:
Truth has never been determined by “an overwhelming consensus,” and in fact, consensuses have often been completely wrong.

Karoly:
… climate model simulations have been used to assess the relative importance of different forcing factors on the climate system and how well they explain the observed global warming. The simulations are driven by natural forcing factors, such as changes in solar radiation and volcanic aerosols, as well as human-caused changes in greenhouse gases and human activity-related climate forcing factors, including industrial aerosols and land use change.

Happer over deze grafiek:
The important message of this Fig. is that CO2 concentrations have been much higher than present values over most of the history of life. Even though CO2 concentrations were measured in thousands of parts per million by volume (ppm) over most of the Phanerozoic, not the few hundred ppm of today, life flourished in the oceans and on the land. Average pH values in the ocean surface were as low as pH = 7.7, a bit lower than the pH = 8.1 today. But this was still far from acidic, pH < 7, because of the enormous natural alkalinity of seawater. The mean global temperature was sometimes higher and sometimes lower than today’s. But the temperature did not correlate very well with CO2 levels. For example, there were ice ages in the Ordovician, some 450 million years ago, when the CO2 levels were several thousand ppm. …

Karoly:
The observed significant cooling for one to two years after major volcanic eruptions —Santa Maria (1903), Agung (1963), El Chicon (1982), and Pinatubo (1991) —is simulated very well. The observed global mean temperature variations throughout the whole period lie within the range of all the model simulations with combined forcings, indicating the models simulate well the chaotic interannual variability of global mean temperature. There is very good agreement between the observed long-term global warming since the late nineteenth century and the average global warming across all the model simulations for combined natural and anthropogenic forcing. …

Of course, a small number of scientists say that the climate models are tuned to simulate the recent observed warming but are unreliable for projecting future warming trends. Others say that they show too much global warming, because the observed warming from 1998 to 2010 was very small, while the simulated warming continued, if you consider the average across all the climate model simulations. As shown already when considering the observed global mean temperature variations, there is large natural variability in global mean temperature in the observations and the models. The observed departure in 2010 from the multi-model mean is no larger than in 1910 or in 1940 and is well within the envelope of all the model simulations.

I disagree. This statement is based on excessive faith in computer models. The wide availability of computers and powerful software to make color displays has been a serious problem, since it has blurred the lines between reality and virtual reality. These are not the same. In my Statement and Interview I tried to stick to real satellite pictures of visible and thermal radiation from the Earth, real measurements of ocean pH, real records of tornados, hurricanes, floods, droughts, etc. Essentially all of Dr. Karoly’s claims of warming from greenhouse gases come from computer models, with lurid, threatening reds to represent the supposedly harmful effects of the demon gas, CO2.

Karoly:
Global warming has led to increases in hot extremes and heatwaves, affecting human health and leading to crop and animal losses, as well as increases in the occurrence and intensity of wild fires in some regions.

Increases in global temperature have led to global sea level rise, flooding coastal areas and causing coastal erosion and pollution of coastal freshwater systems with seawater. The impacts of storm surges, combined with global and regional sea level rise, were clearly demonstrated by the storm surge impacts of Hurricane Sandy on New York City and the east coast of the United States. Expected sea level rise by the end of this century for even the smallest projected global warming will lead to the annual flooding of many hundreds of millions of people and the complete loss of some low-lying island countries.
One of the other major impacts of climate change due to increasing carbon dioxide concentrations is the increase in carbon dioxide dissolved in the oceans. As shown below, the dissolved carbon dioxide in the upper waters of the ocean has increased in parallel with the increase in atmospheric concentration. As the oceans absorb more carbon dioxide, they become less basic (or more acidic), with a higher concentration of carbonic acid. This can be seen in the decrease in pH of ocean water by about 0.1 units over the last 30 years.

The increase in carbon dioxide concentrations in the atmosphere has some potential benefits for plants because carbon dioxide is essential for photosynthesis. Plants grown in an atmosphere with higher carbon dioxide have faster growth rates and lower water use, assuming there are no other limits on growth.

Happer:

If increasing CO2 causes very large warming, harm can indeed be done. But most studies suggest that warmings of up to 2 K will be good for the planet [ (Tol 2009)] extending growing seasons, cutting winter heating bills, etc.

More CO2 in the atmosphere will be good for life on planet Earth. Few realize that the world has been in a CO2famine for millions of years — a long time for us, but a passing moment in geological history. Over the past 550 million years since the Cambrian, when abundant fossils first appeared in the sedimentary record, CO2 levels have averaged many thousands of parts per million (ppm), not today’s few hundred ppm, which is not that far above the minimum level, around 150 ppm, when many plants die of CO2 starvation [(Dippery, et al. 1995)]. An example of how plants respond to low and high levels of CO2 is shown in Fig. [7] from the review by Gerhart and Ward.” (Gerhart and Ward 2010)

Tamblyn:

Temperature — specifically leaf temperature — is a critical factor in photosynthesis and crop yields. Photosynthesis is temperature-dependent: the productivity of photosynthesis is poor at low temperatures, rising to a peak around 30° C for C3 photosynthesizers, slightly higher for C4 plants. Beyond this peak, photosynthesis efficiency declines markedly, dropping to very low by around 40° C.

Happer:

I believe that more CO2 is good for the world, that the world has been in a CO2 famine for many tens of millions of years and that one or two thousand ppm would be ideal for the biosphere. I am baffled at hysterical attempts to drive CO2 levels below 350 ppm, or some other value, apparently chosen by Kabbalah numerology, not science.

Over most of the geological history of the Earth, CO2 levels have been much higher than now. There were no tipping points: ocean acidification was not a problem; corals flourished, leaving extensive fossil reefs for us to study today; and evolution continued its steady course on land and in the oceans, punctuated by real catastrophes, including giant meteor strikes, massive volcanic eruptions leading to vast areas of flood basalts, etc. These events probably released CO2, CH4, SO2, and other gases that significantly affected the oceans and atmosphere, but the catastrophes were not directly caused by greenhouse gases. … The only undisputed effect of more atmospheric CO2 over the past century has been a pronounced greening of the earth …

One of the bogeymen is that more CO2 will lead to, and already has led to, more extreme weather, including tornadoes, hurricanes, droughts, floods, blizzards, or snowless winters. But … the world has continued to produce extreme events at the same rate it always has, both long before and after there was much increase of CO2 in the atmosphere. In short, extreme weather is not increasing. [Original reference (Pielke Jr. 2017)]

We also hear that more CO2 will cause rising sea levels to flood coastal cities, large parts of Florida, tropical island paradises, etc. The facts, from the IPCC’s Fifth Annual Report (2013), are shown in Fig. 19 [not reproduced here]. A representative sea level rise of about 2 mm/year would give about 20 cm or 8 in of sea level rise over a century. For comparison, at Coney Island, Brooklyn, NY, the sea level at high tide is typically 4 feet higher than that at low tide …

In biologically productive areas, photosynthesizing organisms remove so much CO2 during the day that the pH can increase by 0.2 to 0.3 units, with similar decreases at night when respiring organisms return CO2 to the water.

The simplest interpretation of the discrepancy of [this graph] is that the net feedback is small and possibly even negative. … Is concerted governmental action at the global level desirable? No. More CO2 will be good for the world, not bad. Concerted government action may take place anyway, as has so often happened in the sad history of human folly. … It is immoral to deprive most of mankind of the benefits of affordable, reliable energy from fossil fuels on the basis of computer models that do not work.

From Phil Jones To: Michael Mann (Pennsylvania State University). July 8, 2004
“I can’t see either of these papers being in the next IPCC report. Kevin and I will keep them out somehow — even if we have to redefine what the peer-review literature is!”